.25 ultra se , longer barrel req

[clintwestwood]

hi guys.

i'm looking to swap out the pathetic tiny barrel on my bsa ultra se to a longer barrell , am i correct in assuming any barrel in the ultra rage will fit? (as long as its got the 2 milled flats on it for the grubscrews?

or indeed is there any others that will fit?

i'm kinda struggling to find a bsa ultra long barrel in .25  here in the uk.

i want to keep it in .25 cal , i just want a longer barrel.


thanks in advance.


dave.

[subscriber]

Dave,

Not to heckle you, but is your BSA a sub-12 foot.pound PCP?  If so, the longer barrel would help only, if your mission is to improve the appearance over what you have.   Certainly, slow .25 pellets that spend more time in the barrel will actually make shooting well, more difficult for you, because of longer "barrel time". 

Rather than sabotage your mission, I would like to suggest that you add a shroud to the barrel, that extends past the actual barrel muzzle.  If you have access to a 3D printer, I would be happy to design and air stripper and baffles to install into that shroud, so it is fully functional, as well as pretty.

To help you, I would need a number of landmark dimensions, including how long a barrel you would choose, if any length were available?  As measured from the front of the receiver for the purpose of designing a shroud.   Next, how large a barrel outside diameter would you choose, assuming you wanted to achieve a "bull-barreled" look.  The actual barrel OD and the existence and specs of any threads at the muzzle would be next? 

If you have a moderator installed and want to keep it, then extending the shroud would become a bit more involved.  Else, a longer shroud that is smaller in diameter than your moderator, but at least 8 mm larger in outside diameter than the barrel OD would be indicated.  So, for a 16 mm barrel OD, the shroud OD would be a minimum of 24 mm. 

Now, I would choose the shroud tube based on reasonably priced carbon fiber or thin walled aluminium tubing available in your area.  That might be 25 mm, or an inch.  If the barrel OD is 15 or 11 mm, then the shroud tube could be smaller in OD.  Although, there is also the internal volume that factors in.  So, my default answer would be 25 mm OD or an inch.

Part of that equation is the space between the barrel OD and the air tube or tank.  I would prefer to keep things simple with a coaxial shroud, although I have done a few offset designs, such as this one: https://www.gatewaytoairguns.org/GTA/index.php?topic=209016.msg156461334#msg156461334




Unless you are good at fabrication, I would stick with coaxial designs.

By the way, a simple tube that has an ID fit snugly with the barrel OD to make the barrel look longer might work.  But generally, the air in such a tube will flow past the pellet from the rear on the shot, and upset the pellet stability while traveling in the tube extension.  That would tend to open up groups, but you could try it, if you have some tubing handy.

I might be mistaken, but I think that BSA may have related airgun models that have shrouded barrels.  The best option (but perhaps not the cheapest) would be to purchase a factory shrouded barrel; or a factory shroud compatible with your barrel and receiver.  You could contact BSA and ask them.

Food for thought?

[subscriber]

Dave,

It is unlikely that any US forum member would be able to ship you a barrel, due to import/export limitations on such parts.  If you can't find a suitable barrel in the UK or EU, then there is another option "in your backyard": 

The gent in the videos below could either machine a longer barrel to fit your BSA; and / or make you a shroud for it.  At the very least, he could advise you:











With my offer, I would share only CAD or print files.  All materials sourced and parts made would need to happen at your end.  So, unless you did or managed that yourself, you might get someone such as the chap in the video to do it for you; using his own approach and designs.

[clintwestwood]

hey hi!

wow, what a lovely reply.
you're such a gentlman, thank you so much for getting back so fast!

i'm actually an engineer for work , and i've a machine shop at home (lathe etc).

i do see what you mean, could i not just get a longer barrel and then re tune him up to uk (wimpy) limit? 
i just don't know as much as you buddy.
if i did manage to obtain a longer barrel, re tune to uk pea shooter legal power, would this improve accuracy or just make the power curve fall too fast?
obviously i have to keep it to the uk limit of 12 fbs.
i do remember seeing in a magazine when i was a kid, they experimented with an old springer, kept cutting the barrel down, and in the end the action broke due do exess power.
so i think im right in thinking longer the barrel, more power req to gain the same muzzle energy?

i just thought a longer barrel may improve accuracy.


once again,  thank you sir for such a kind , well wrote reply.


all my very best to you.

dave.

[subscriber]

Dave,

If you obtained a longer quality barrel such as the hammer forged one in your BSA, then the muzzle velocity is likely to be higher than for the stock barrel, but not by very much.  Most of the pellet acceleration would be happening in perhaps the first third of your existing barrel; and with a longer barrel, the pellet would be almost coasting for half its length.  That is, until you crank the power up.  Which, as far as we are concerned, you are not planning to do.

Now, depending on what weight pellet you are using in .25, the velocity at 11.5 FPE is likely to be low.  For a 25.4 grain pellet at 450 FPS you would be at 11.4 FPE.  A 19 grain pellet at 525 FPS would yield 11.6 FPE.  A 34 grain pellet at 390 FPS would yield 11.5 FPE.

So, if you compared .25 pellet velocity to a .177, with both at 11.5 FPE, then the lighter but typical .177 pellets would be travelling almost twice as fast as the .25 pellets.  This is useful for a flatter trajectory and makes range estimation more forgiving.  It also reduces the time the pellet spends in the barrel, where you could "steer it off course" while the pellet is traveling down the barrel.  Now, the importance of the latter may be overblown, if you are good at shooting spring piston air rifles.  Just apply the same exaggerated follow through and you will be better than fine.

You could absolutely machine the longer barrel from a blank or donor air rifle, yourself.  All you need to do is measure the section of the barrel that fits into the receiver socket and duplicate the features machined into the stock barrel.  This includes the chamber end with a transfer port (unless there is a separate thimble part containing the TP).  The TP would be at the bottom of the barrel, with the retention screw flats or dimples at the top.

You will find a lot of advice on how to chamber and crown barrels properly on this forum.  This barrel improvement guide is a good place to start:  https://www.gatewaytoairguns.org/GTA/index.php?topic=130555.0

Depending on your lathe, and how concentric the chuck or collet runs, you may need to use some fixtures or apply some techniques to get the bore of the barrel to run true, before you machine any features.  You might just use a four jaw chuck and a clock gauge, reading a gauge pin in the bore (or the land tops directly), after deburring the bore at the squared off barrel face.

This section of the forum, and the people that frequent it have made many custom PCP airguns from scratch, so they will be very capable of offering good advice to you.

[subscriber]

About the accuracy question, Olympic target PCPs often have short barrels, with a long tube over it, to elongate the sight radius.  But that is for peep sights, using a front sight.  For low power, a massively long barrel won't always increase accuracy, although if not overdone it does seems to narrow velocity spread. 

Consider the specs for this high end target PCP rifle.  The barrel is 420 mm long.  The sight radius is adjustable from 620 tp 897 mm.  Clearly, most of the tube that looks like the barrel is not actually the barrel:
https://www.krale.shop/us/anschutz-9015-one-basic/

The devil is in the details.  How long a barrel are we taking about in your case?  The Air Arms (CZ made) T200 has a 19" long barrel and is know for being a good shooting PCP, that is also easy to use.  Even at only 5.5 FPE.

In general, longer barrels of a given diameter are less stiff and more "whippy" than shorter barrels.  That can make the vibration harmonics of longer barrels a more significant factor in the way of shooting small groups.  Skinny barrels may also be more pellet fussy; meaning it only shoots some pellets well.  The more powerful the airgun, the worse this barrel whip effect tends to be.

[clintwestwood]

you sir are a legend!

ive researched the barrell whipping theory, yes, its amazing watching this in slo mo.

i can't thank you enough for your expert advice.

thank you so much.


dave

[rkr]

BSA Scorpion SE uses 15" barrel in .25 although finding one would be a nightmare. You will get more shots / fill with longer barrel but it is unlikely to be any more accurate if your current barrel is good. There are also 18.5" BSA barrels and barrel blanks but currently BSA uses all the barrels they make so getting LW blank and machining it is probably your best bet for longer barrel.